Awe-inspiring design of Warragamba Dam

“When you are designing something you need to understand where does this fit in the landscape? What impact will the landscape have on me? What impact will I have on the landscape?” Mary said.

“The answers to these questions are pretty obvious when you are building a dam like Warragamba – you need to know how big to build the dam, how much water will flow down the rivers to the dam, how much water do I need it to hold, how much do I need it to release during floods?

“But these are the same questions we should be asking for everything from urban planning and rural farming practice to recreational opportunities and natural area management.

“If we plan and design urban landscapes and developments well, we can reduce and sometimes improve the health of the natural environment. If urban development is done poorly, the health of our catchment declines.

“Water sensitive urban design is the integration of water management into planning, design and construction of the built environment. For example, ensuring stormwater from the built environment is filtered and slowed down before it enters our streams to ensure that nutrient and sediment are retained higher in the landscape and not within our waterways.

“In the rural landscape, we design practices that reduce impacts on our streams and waterways. Examples include adjusting grazing intensity to maintain groundcover, and excluding stock from riparian areas which creates a buffer so you don’t lose nutrients into the creeks and rivers,” Mary said.

Brian Mayhew, General Manager Regional Operations Sydney, spoke about how the Warragamba River offered two important advantages as a site for a major dam: a large catchment area, and a river flowing through a narrow gorge.

“This meant a tall and narrow dam capable of holding a vast amount of water could be built,” Brian said. “The designers spent four years on site investigations including drilling bore samples to understand the geology of potential dam sites, and settled on this site.”

Brian described the huge forces in play holding back more than 2,000 gigalitres of water: “The pressure behind the dam is in effect trying to push the wall down the valley, at the same time as water in the rock under the dam is trying to push it up. The designers took these water pressure and uplift pressures into account in designing this concrete gravity dam.”

The dam was built in a series of large interlocking concrete blocks. Overhead cableways lifted 18 tonne buckets to carry concrete across the Warragamba Gorge to build each block. Ice was mixed with the concrete to control heat generation and prevent cracks.

Two temporary (coffer) dams and a tunnel were built to divert the Warragamba River and keep the site dry so excavation for the dam could start. Concrete was mixed on site using 305,000 tonnes of cement and 2.5 million tonnes of sand and gravel. Sand and gravel were transported from McCann's Island in the Nepean River via an aerial ropeway.